Without going really big, I don't know how to do this. So far I use a Roland Mobile AC amplifier. It's just 5 watts, but it sounds beautiful and it's tiny, fits in my backpack, powered by 6AA batteries, with my cords and headset microphone from Audio-Technical, and my acoustic guitar in one hand, I have a very travel friendly busking setup. I actually traveled several cities with it. Just a backpack and guitar, including some change of clothes.

BUT SOMETIMES it is too quiet. I bought a Roland AC-33, also beautiful sound, but on batteries it is only 20W per Roland, and it doesn't sound much louder at all. Certainly not loud enough to justify double the space and that much more weight and 4x the price! Plugged into an AC socket it says to give 30W power. But I usually don't have a place with a socket.

Anyhow, again Roland has a CUBE Street Ex with 50 W power, the only problem (in addition to more weight) is the sound is just not as good for acoustic guitars. It makes no sense because most of the time I see people using it for Acoustic guitars and vocals. Anyhow, that and the price is $500, so now it's 5x the little mobile AC amp, which sounds good and is great for many places.

1) So is there a way to get the extra 10W out of the Roland AC-33 without an AC socket?
2) How much wattage do I really need typically for when I'm on the street and there is traffic noise, buses, and so forth?
3) How much more volume can I get from a 40 or 50W combo amp/PA? Or do I need 100W?
(I'm considering a Behringer Europort 40W (8 inch speaker) or 100W (6 inch speaker).)

4) Is there a "thinking outside the box" solution where I can have a really small lightweight amp like Mobile, but louder.

5) I just got a Boss VE-8, which has a pre-amp and effects. Will this increase volume?

2 Answers
2

This is a very difficult question to answer. It comes down to "how loud is loud enough" which is the same is "how long is a piece of string"

So let me try answer in a generic way.

Sound Pressure Level

Often people mix terms like "power or watts" with "loudness" of a system. And generally speaking a system with more "watts" would be louder than a system with less... but this is not really the case.

First of all the speaker design is very much part of how "loud" a sound it can produce, and this is measured, and called SPL (Sound Pressure Level)

Usually this is captured (in dB) by sending 1 Watt of power into a speaker, at a particular frequency, measured 1 meter in front of the speaker.

Example, you could have a speaker which is SPL 90 dB (at 1 Watt, at 1 meter, at 1000 Hz)

This means the speaker is producing 90 dB under those circumstances. Every doubling of Watt, is an increase of 3dB in SPL:

2W = 93db

4W = 96db

8W = 99db

16W = 102db

32W = 105db

64W = 108db

128W = 111db

The amplifier behind the speaker is "just driving the speaker", up-to the maximum of speaker and amp.

By finding out the SPL of the equipment you are considering, you can determine the "maximum loudness" of that particular system.

Perceived Loudness

But this is not all, there is this concept of "perceived loudness". The human ear is not directly related to this technical concept of SPL and doubling in loudness every 3 dB.

While the true measurable SPL may double when you double the wattage, the human ear will only perceive a doubling in loudness every 7-8-9 dB (I do not have references at the moment, someone may comment on this). Meaning that in the worse case scenario; you will need 9 dB increase for a human to perceive a doubling in loudness... which is 8 times the power (all speakers given an equal SPL)

Given this example, your need 160 Watts (given speaker SPL equal), compared to your now 20 Watts, to have a perceivable doubling of "loudness".

I hope that this explains why your perception of loudness increase between the original 20 Watts and the 30 Watts is not according to your expectation of the 50% power increase. This 50% increase in Power (give SPL of the speakers equal) would result in 1.76 dB increase of SPL, which is far too low for the human ear to capture as significant.

[EDIT]
I just found a reference here, scroll down to "Human perception of loudness", and you see that this reference actually puts that at 10 dB (10 times the Power) for doubling of loudness.

Closing remarks

Finally, I would like to say, more power requires more battery capacity, more electronics, bigger boxes, and will be more expensive.

I am not an expert in open-air, street performance, and cannot offer you an opinion on "how loud" you need to be to overcome environment noise/sound.

Unfortunately, not all vendors lists their SPL in the manual, for the Roland AC 33, it is not listed in the manual, which means you need to call them to find out.

When there is loud traffic noise, go somewhere more quiet. If you try to be louder than loud noise, you'll be poisoning the well for busking. If loud noise is annoying to shops and people living there, busking in excess of traffic noise is going to be more annoying. Also where there is loud traffic noise, there will not be enough room for people to stand and listen and ultimately put some coins in your case.

Like with perfume, the point of busking is not to announce your presence to as wide a crowd as possible while keeping them at a large distance, but rather to make them want to come close enough to interact with you.